Abstract
A study was performed to examine any effect of hen age on the feeding ability and mortality of different life-stages of Dermanyssus gallinae [Poultry Red Mite (PRM)] when fed using a high welfare, on-hen mite feeding device. Mite feeding assays were carried out every two weeks on a cohort of five Lohman Brown hens with devices containing adult and deutonymph PRM or adult and protonymph PRM. Feeding rates and mortality of each PRM life stage and oviposition of adult female PRM were evaluated over an 18-week period. There was a significant reduction in oviposition rates of female PRM as they fed on hens of increasing age. However, no clear trend was detected between the feeding rates of all three haematophagous life stages and hen age. The same conclusion was reached regarding mite mortality post-feeding in both deutonymph and adult female PRMs, although a weak positive association was apparent between hen age and protonymph PRM mortality. This study shows that the on-hen feeding device can be used both for short term studies to assess novel anti-PRM products (new acaricides, vaccines etc.) and longer, longitudinal studies to determine longevity of the effects of such novel anti-PRM products. It also demonstrates that blood feeding by mites on older hens is less able to sustain PRM populations than feeding on younger hens. This on-hen mite feeding device directly impacts upon reduction and refinement by greatly reducing the numbers of birds required per experimental group compared to traditional PRM challenge infestation models and by eliminating the need for birds to be exposed to large numbers of mites for extended periods of time that can cause welfare concerns. This paper describes the methodology for these studies and how to assemble pouches and handle mites both before and after feeding assays.
Highlights
Poultry red mite (Dermanyssus gallinae De Geer, 1778) costs the hen egg-laying industry in excess of €231 million per year in the European Union (Flochlay et al, 2017) and is a major welfare problem in the egg laying industry where the birds are kept in situ for long periods of time (~1 year) allowing them to form large populations in the hens’ accommodation
This method offers an alternative to the in vitro tests, to allow much more accurate and reliable assessment of vaccines and other mite control methods on small numbers of hens before progressing to field studies. This strategy addresses the “Reduction” aspect of the 3Rs principles by greatly reducing the number of hens used, as it would accurately discriminate between effective and poorly-performing vaccines or other control methods before they were progressed to field trials. We propose that this on-hen system may be used to test the effectiveness of mite control methods across prolonged periods on small numbers of hens (
Comparison of feeding by mite life stage and time point There were statistically significant overall effects of mite lifestage and of the interaction between this and time on the proportions of mites feeding on hens when applied to the hens in the feeding devices (p < 0.0001 in each case) (Nunn et al, 2020a)
Summary
Poultry red mite (Dermanyssus gallinae De Geer, 1778) costs the hen egg-laying industry in excess of €231 million per year in the European Union (Flochlay et al, 2017) and is a major welfare problem in the egg laying industry where the birds are kept in situ for long periods of time (~1 year) allowing them to form large populations in the hens’ accommodation. This blood-feeding ectoparasite has a five-stage life cycle (Figure 1) and the protonymph, deutonymph and adult stages are all haematophagous, feeding on the hens at night time. These include Salmonella Enteritidis (Sparagano et al, 2014) and avian influenza virus (Sommer et al, 2016) and PRM has been demonstrated to act as a reservoir for fowl typhoid between sequential hen flocks (Pugliese et al, 2019)
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